OFFSET
1,1
COMMENTS
Numbers k such that A007913(sigma(k)) is equal to A007913(2*k), thus numbers for which sigma(k) has the same set of distinct prime factors with an odd exponent as 2*k.
Among the first 257 terms, these four are also in A228058:
46277101 = 61 * 13^2 * 67^2,
49889853 = 13 * 3^2 * 653^2,
106706925 = 13 * 3^2 * 5^2 * 191^2,
676830973 = 37 * 7^2 * 13^2 * 47^2.
LINKS
EXAMPLE
MATHEMATICA
Select[Range[10^6], SameQ @@ Map[Sqrt[#] /. (c_: 1)*a_^(b_: 0) :> (c*a^b)^2 &, {DivisorSigma[1, #], 2 #}] &] (* Michael De Vlieger, Feb 08 2020, after Bill Gosper at A007913 *)
PROG
(PARI) isA331752(n) = (core(2*n)==core(sigma(n)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Feb 06 2020
STATUS
approved